(1) Field of the Invention
This invention relates to a signal input sheet used to input a signal at a desired position of a sheet surface in response to pressure of said position.
(2) Description of the Prior Art
Various online real-time character recognition devices have been known which recognize information while describing the information to input hand-written information (see Japanese Patent Application Laid-Open Nos. 56-124973 and 56-124976). As hand-written information input devices used for these devices, various sheet-like input devices have been known which utilize distortion of a sheet surface due to the writing pressure when informatiion is described on the sheet surface to obtain a position signal with the variation of writing order.
In this sheet-like input device, it is designed so that a conductive surface is positioned in an isolated state on a basic resistance surface which is a detecting base plate, and the conductive surface comes into contact with the basic resistance surface according to writing pressure to form a variable electric circuit to sequentially obtain position signals. Known as the isolated structure of the conductive surface to the basic resistance surface includes an arrangement of pressure sensitive conductive rubber in which a conductive material is discontinuously distributed into a rubber material so that at writing pressure, the conductive material may obtain a conductivity continuously, and an arrangement of the meshes of a net in which a sheet bored with holes such as the meshes of a net is intersposed between the basic resistance surface and the conductive surface, and at writing pressure, the conductive surface comes into contact with the basic resistance surface through the meshes of a net to obtain a conductivity (see Japanese Patent Publication No. 59-7992).
Generally, a signal input sheet is extended on a detecting surface of the hand-written information input device, as described above, and information is written into the signal input sheet. In this case, human hands inevitably touch the signal input sheet, and therefore, there poses disadvantages that electric charge charged in a human body, so-called static electricity passes through the signal input sheet to affect the device body, materially lowering a recognition rate and image resolution due to the disturbance of input information.
Furthermore, in the arrangement of pressure sensitive conductive rubber in the aforementioned signal input sheet, in the manufacture of conductive rubber, unevenness occurs in distribution of a conductive material. Where in use, a pressure area is wide, there is less problem but in case of variation in pressure of a small area such as writing pressure, the desired conductivity is hard to obtain to pose various problems. Moreover, where a writing area is wide, materials of conductive rubber having high precision and high quality are required but ones having a wide area are hard to obtain, resulting many inconveniences in terms of technical and economical terms.
In the arragement of a sheet of meshes of a net, the sheet itself has a discontinuity, and therefore, a portion for obtaining a conductivity is discontinuous. In those to which is applied longitudinal, lateral and oblique writing pressure, if the pressure is applied to a continuous portion of the sheet, it is not possible to obtain the conductivity, and also in case a continuous signal of high density is obtained, it is impossible to do so.